Applicants"" invention relates to electrical telecommunication, and more particularly to wireless communication systems, such as cellular and satellite radio systems, for various modes of operation (analog, digital, dual mode, etc.), and access techniques such as frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and hybrid FDMA/TDMA/CDMA. More specifically, this invention relates to slot formats for transmissions between a communication system and a mobile station on a packet data channel.
FIG. 1(a) shows a general example of a forward (or downlink) digital control channel (DCCH) configured as a succession of time slots 1, 2, . . . , N, . . . included in the consecutive time slots 1, 2, . . . sent on a carrier frequency. These DCCH slots may be defined on a radio channel such as that specified by TIA/EIA/IS-136, and may consist, as seen in FIG. 1(a) for example, of every n-th slot in a series of consecutive slots.
As shown in FIG. 1(a), the DCCH slots are organized into superframes (SF), and each superframe includes a number of logical channels that carry different kinds of information. One or more DCCH slots may be allocated to each logical channel in the superframe. The exemplary downlink superframe in FIG. 1(a) includes three logical channels: a broadcast control channel (BCCH) including six successive slots for overhead messages; a paging channel (PCH) including one slot for paging messages; and an access response channel (ARCH) including one slot for channel assignment and other messages. The remaining time slots in the exemplary superframe of FIG. 1(a) may be dedicated to other logical channels, e.g., additional paging channels (PCH).
FIG. 1(b) illustrates an exemplary information format for the slots of a forward DCCH. Therein, the number of bits in each field is indicated below that field. The bits sent in the SYNC information are used in a conventional way to help ensure accurate reception of the CSFP and DATA fields. The SYNC information carries a predetermined bit pattern used by the mobile stations to find the start of the slot. The SCF information is used to control a random access channel (RACH), which is used by the mobile stations to request access to the system. The CSFP information conveys a coded superframe phase value that enables the mobile stations to find the start of each superframe.
The systems currently specified by the TIA/EIA/IS-54 and TIA/EIA/IS-136 standards are circuit-switched technology, which is a type of xe2x80x9cconnection-orientedxe2x80x9d communication that establishes a physical call connection and maintains that connection for as long as the communicating end-systems have data to exchange. The direct connection of a circuit switch serves as an open pipeline, permitting the end-systems to use the circuit for whatever they deem appropriate. While circuit-switched data communication may be well suited to constant-bandwidth applications, it is relatively inefficient for low-bandwidth and xe2x80x9cburstyxe2x80x9d applications.
Packet-switched technology, which may be connection-oriented (e.g., X.25) or xe2x80x9cconnectionlessxe2x80x9d (e.g., the Internet Protocol, xe2x80x9cIPxe2x80x9d), does not require the set-up and tear-down of a physical connection, which is in marked contrast to circuit-switched technology. This reduces the data latency and increases the efficiency of a channel in handling relatively short, bursty, or interactive transactions. A connectionless packet-switched network distributes the routing functions to multiple routing sites, thereby avoiding possible traffic bottlenecks that could occur when using a central switching hub. Data is xe2x80x9cpacketizedxe2x80x9d with the appropriate end-system addressing and then transmitted in independent units along the data path. Intermediate systems, sometimes called xe2x80x9croutersxe2x80x9d, stationed between the communicating end-systems make decisions about the most appropriate route to take on a per packet basis. Routing decisions are based on a number of characteristics, including: least-cost route or cost metric; capacity of the link; number of packets waiting for transmission; security requirements for the link; and intermediate system (node) operational status.
Packet networks, like the Internet or a corporate LAN, are integral parts of today""s business and communications environments. As mobile computing becomes pervasive in these environments, wireless service providers such as those using TIA/EIA/IS-136 are best positioned to provide access to these networks. Nevertheless, the data services provided by, or proposed for, cellular systems are generally based on the circuit-switched mode of operation, using a dedicated radio channel for each active mobile user.
However, the Cellular Digital Packet Data (CDPD) System Specification, Release 1.0 (July 1993), which is expressly incorporated herein by reference, describes a concept for providing packet data services that utilizes available radio channels on current Advanced Mobile Phone Service (AMPS) systems, i.e., the North American analog cellular system. This specification covers functionality topics such as external interfaces, air link interfaces, services, network architecture, network management, and administration.
The specified CDPD system is, to a large extent, based on an infrastructure that is independent of the existing AMPS infrastructure. Commonalities with AMPS systems are essentially limited to utilization of the same type of radio frequency channels and the same base station sites (the base station used by CDPD may be new and CDPD specific) and employment of a signalling interface for coordinating channel assignments between the two systems.
Despite the advent of CDPD, there still exists a need for a system providing general purpose packet data services in digital (e.g., DAMPS, IS-136) cellular systems, based on providing shared packet-data channels optimized for packet data. This application is directed to systems and methods that provide the combined advantages of a connection-oriented network, like that specified by the TIA/EIA/IS-136 standard, and a connectionless, packet data network. Furthermore, the present invention is directed to techniques for accessing a wireless packet data network, for example, using existing connectionless network protocols with low complexity and high throughput.
According to one embodiment of this invention, a communication system supplies packet control channel feedback information to mobile stations communicating with the system which is responsive, among other things, to bursts of packet data information transmitted by the mobile.
It is an object of one exemplary embodiment of this invention to provide maximum efficiency of the packet data channel by providing means for interrupting transmissions so as to allow for transmissions from other mobile stations that are either attempting to access the system or have already accessed the system and are in the process of sending packet data information. According to the present invention, the packet control channel feedback information includes several flags: Received/Not Received (R/N); Partial Echo (PE); and Partial Echo Qualifier (PEQ). The PEQ allows the communication system to interrupt the transmission from one mobile station to allow for transmissions from another mobile station. By setting the PEQ to various values, the communication system can dynamically allocate ownership of the RACH subchannels and thereby indicate to mobile stations whether or not their subchannel ownership has been temporarily interrupted and reassigned to another mobile station.
In particular, PEQ values have been optimized according to exemplary embodiments to: (1) release the BRI field of the existing IS-136 physical layer for other functionality, (2) allow for a contention-based access scheme (e.g., Slotted ALOHA or CSMA) to operate concurrently with the multiplexing feature (reservation-based access) on the uplink of the same channel, (3) provide for equal application of delay to all packet data users on the same channel independent of loading and (4) quickly detect and recover from subchannel hijacking.